1. Field of the Invention
The present invention relates to methods for forming titanium alloy materials, and more particularly to a method of forming titanium aluminide materials using conventional sheet metal equipment and tooling to fabricate structural components, and localized heating of the workpiece alone.
2. Background of the Invention
In the family of intermetallic metals, titanium aluminide materials have become most useful in the design of structures requiring a high strength-to-weight ratio. Although unique in the class of titanium alloy compositions, titanium aluminide materials may, like the more typical titanium alloys, contain additions of one or more alloying agents such as tin, zirconium, molybdenum, vanadium, silicon, chromium, manganese and iron. Titanium aluminide materials find particular application in the field of aircraft and spacecraft design.
While several important end uses exist for titanium aluminide materials, there still remain various difficulties in effecting deformation of these materials to achieve a final, desired useful shape. The most frequently encountered obstacle is the inability to manipulate these materials, for it has become well-known that titanium aluminides are relatively brittle and not amenable to forming with conventional techniques at or near room temperatures.
One recent approach which has found widespread utility in the fashioning of structural components from such materials is superplastic forming, a process in which a superplastic material (e.g., a titanium or aluminum alloy) is heated to a forming temperature, generally in the range of from about 1700.degree. F. to about 1900.degree. F., and then formed in a die using positive or negative pressure on one side of the metal to force the metal to plastically "flow" against or into the die.
Although the advantages of superplastic forming are numerous, the process has drawbacks. For one thing, it requires special equipment including a controlled environment within the heating and forming apparatus, the application of very high forming temperatures (on the order of about 1700.degree. F. to about 1900.degree. F.), and specially designed tools for handling the materials and equipment while heated and before they are fully cooled. Additionally, the heating and cooling phases of the process take place over extended periods of time and require uniquely designed tool supports having appropriate thermal coefficients to accomodate the high forming temperatures. For these reasons, as well as the fact that this process requires thermal treatment of not only the whole workpiece, but also the heating and forming apparatus, efforts have been made to discover alternative techniques and/or equipment to achieve the same or similar end results, while reducing cost and time involved and increasing efficiency.